Electrothermic indicating apparatus



March 1, 1960 K. T. KALLE 2,927,308

ELECTROTHERMIC INDICATING APPARATUS Filed NOV. 7, 1957 2 Sheets-Sheet l KARL T. KALLE INVENTOR ax/M, e

March 1, 1960 V K. TL KALLE 2,927,308 ELECTROTHERMIC INDICATING APPARATUS Filed Nov. 7, 1957 2 Sheets-Sheet 2 31 29 I 12 III! 11 KARL T. K'ALLE INVENTOR United States Patent Ofiice 2,927,308 Patented Mar. 3, 1960 2,927,308 ELECTROTHERMIC INDICATING APPARATUS Karl Torsten Kalle, Sandbacken, Saffle, Sweden Application November 7, 1957, Serial No. 695,045 Claims priority, application Sweden December 5, 1956 4 Claims. (Cl. 340-201) The invention relates to an electrothermic indicating apparatus for indicating pressures, temperatures, the position of a body in motion or any other physical state capable of generating a movement. The apparatus is of the known type which comprises in combination an electric circuit containing two cooperating movable first and second contacts, a motion transmitting member supporting the first contact and arranged to be acted upon by the magnitude to be measured, thereby adjusting the position of said first contact in relation to the second contact, a thermoresponsive heating element subjected to variations in length when heated and connected to cause thesecond contact to open and close the circuit in dependence on such variations in length, means for heating said element when current passes the circuit, and a pointer instrument connected to show a deflection in dependence on the effective value of the current pulses produced by the opening and closing operations of the contacts.

' A drawback of this otherwise effective apparatus is that after some time of use the two contacts run the risk of becoming dirty or being coated with thin films of oxide owing to spark formation, whereby the current'conduction is rendered more difiicult or even impossible. Es-

pecially serious troubles may arise in case the contacts permit a certain, limited current conduction so that the apparatus seems to operate quite normally, although the values indicated are nevertheless faulty. Such a minor defect can be present for a long time without being vdiscovered, which may cause disturbances in the processes or functions to be controlled by the apparatus.

According to the invention, these risks are now substantially eliminated in that one of the contact members is connected to an electromagnetically operated vibrator which causes said contact to vibrate in a direction substantially perpendicular to a line extending through both contact members. By this device every contact between the contact members will thus be combined with a slight lateral gliding motion and although the contact is effected by means of a very light spring pressure, the friction arising between the contact surfaces has proved quite sulficient to efiectively prevent the formation. of insulating coatings. The slight contact pressure causes no visible Wear of the contact surfaces. Generally, one of the contact members is formed as a more or less blunt point, and in such case the vibration causes the rather limited contact surface to shift its place all the time, which highly contributes to a reduced wear as result of the gliding motion.

The device according to the invention will be described more in detail with reference to the accompanying diagrammatical drawings, in which Figure 1 shows a side view of one embodiment;

Figure 2 shows a top view of the essential parts of the device in Fig. 1;

Figure 3 is a fragmentary view of the same device, as seen from the right in Fig. 1;

Figure 4 shows a detail of another embodiment.

It is desired that the apparatus reacts quickly and for this reason it is suitable to use a relatively high current intensity so that the heating of the thermo-responsive element takes place without any noticeable loss of time. Therefore, an alternating current of'e.g. 220 volts tension is converted by a transformer into a current having a tension of 25-30 volts and a correspondingly higher intensity. In the drawing, the transformer is generally designated by 5. As usual, the transformer includes an iron core consisting of metal plates 6, a primary winding 7 and a secondary winding 8. The terminals 9 of the primary Winding 7 are connected to the source of current, whereas the secondary winding 8 feeds the circuit of the apparatus as well as a resistance 10 connected in parallel to said circuit. Preferably the resistance 10 is dimensioned such that the current intensity is equal in both branches. The circuit of the apparatus contains two kind are known,

cooperating contact members 11 and 12 in a series, a resistance 13 causing the change of position of the contact member 11, and a resistance 14 comprised in a pointer instrument.

The contact member 11 has a substantially flat contact surface and is mounted at one end of a rod or a rather rigid Wire 19 which is stretched up to and secured in an upper portion of the support 16. The wire 19 has such a length that the contact member 11 is in its initial position held in close contact with the contact member 12. The heating conductor or resistance 13 consists of a thin, insulated metal wire which is wound around the stretched wire 19. The other heating conductor 14, also consisting of an insulated metal wire, is wound around a rod-like bimetal element 20 which is bent more or less in dependence on its temperature. One

end of the element 20 is secured to a support 21, whereas the free end of said element is arranged to actuate a pointer 22 over a gear transmission not shown. The deflection of the pointer 22 may be read on a scale 23. As various embodiments of indicating instruments of this a detailed description will not be necessary.

A hollow feeler body 24 is inserted through the wall 25 of a room where the temperature is to be controlled. The

- cavity of the feeler body is connected to a bent bourdon V the feeler body 24 may be replaced by a pipe socket.

' holder 27' secured to the free end of situated at some distance from one contact member 12 is mounted (Fig. 3).

pipe 26 projecting from the outer side of the wall. As known, such a bourdon pipe will be bent more or less in dependence on the pressure prevailing therein. If, instead, the pressure inside the wall 25 is to be controlled, A the bourdon pipe 26' carries a thin plate spring 28 which, in turn, supports a plate 29 of iron or some other magnetic metal. The plate spring 28 and the plate 29 are arranged in a common plane end of the iron core 6 and perpendicular to the axis of the windings 7, 8. The end surface of the iron core 6 facing the plate 29 is provided with a transverse groove 39 right between the two windings (see Fig. 3) and the plate 29 is placed outside this groove. Further, the bourdon pipe 26 is arranged to move the plate 29 in its plane in a direction approximately perpendicular to the longitudinal direction of the groove 30.

The plate 29 carries an insulating sleeve 31 in which the Said contact, member has the shape of a pin with a rounded end adapted to engage the flat surface of the contact member 11. The axis of the pin 12 is parallel to the plane of the plate' 29 and perpendicular to the longitudinal direction of the' 11 to one terminal of the secondary winding 8 and a conductor 33 connects the contact member 1 2 to one end of the heating conductor 13.

The groove 30 in the end of the iron core 6 is rather deep to cut off a portion of the magnetic field formed between the windings. This arrangement will result in leakage currents partly deviating outwards from the surface of the iron core and thus actuating the plate 29 which is hereby caused to vibrate with a frequency equal, to the periodicity of the alternating current. Thus, the pin 12 sewing as contact member will move back and forth along the fiat surface of the contact member 12. The amplitude of the vibration need not be great but may amount to about 1 mm, for instance.

Instead of the groove 30 described above, it is also possible to arrange a slot for leakage currents in the Way shown diagrammatically in Figure 4. Two plates 34, 65 are secured, one at each end of the iron core. The plates have their end portions bent towards each other in a common plane in such a way that a space 36 causing leakage currents is formed between the ends of the plates. The plate 29 is arranged right before the space 36, and the function of the arrangement is, in principle, the same as described above. Although the vibration does not become so effective as in the previous embodiment, it might in most cases be quite sufficient.

Except for the vibration device, the apparatus is previously known as a principle and therefore its function needs only a brief description. On supply of current to the primary winding 7 a flow of current is obtained also through the circuitfed by the secondary winding 8, as initially the two contacts :11, 12 are closed. The current teats the resistance wire 13 so that the wire 19 is elongated and the spring 17 causes the contact 11 to break the circuit; The resistance wire 13 will now. be cooled so that the circuit is again closed. As long as the state of the feeler body 24 is unchanged current impulses of mutually equal duration are thus obtained at even intervals and their effective value causes a certain deflection of the pointer 22. The resistance previously mentioned is intended to serve as a kind of condenser to reduce the reduced wear of the contact surfaces. Particular advantages are thus achieved by using a vibrator driven by an electromagnet which is connected to the circuit of the apparatus or to an inductive circuit pertaining thereto. No contact faults whatever have been observed during a long time of use of the new apparatus. A

Generally, the whole apparatus including the transformer is mounted in a common housing. However, if a housing of small dimensions is preferred, it is possible to mount the transformer at some other place, and the housing ,mayin such case'cnclose a small] electromagnet connected to the secondary winding 8 and causing the desired vibration of the contact 12. r

The two contacts 11, 12 need not necessarily be arranged in the same current circuit as the resistances 1 3 and i14 but may, instead, be inserted in the primary circuit, for instance as described in the US. Patent No. 2,551,008.

What I claim is:

1. In an electric indicating apparatus for indicating pressures, temperatures, the position of a body in motion, and similar magnitudes, said apparatus having an alternating current circuit, a motion transmitting member arranged to be acted upon by the magnitude to be measured, a thermoresponsive heating element subjected to variations in length when heated, means for heating said element when current passes through said circuit, and a pointer instrument connected to show a deflection depending on the effective value of the'current pulses produced in the circuit, the combination of afirst and a second movable'contact connected in said circuit and cooperating with each other, the first contact being .supportedby said'motion transmitting member, the position of said first contact thereby being adjustable in relation to. the-second contact, a resilient member supporting the second contact immediately in front of said first contact and connected to said thermoresponsive element to cause the second contact to open and close the circuit depending on the variations in the length of said thermospark formation between the contacts at the momentof breaking.

Now, if the temperature should increase somewhat, straightening of the bourdon pipe this change will result in a tion towards the second contact 11, as soon as the latter has broken the circuit next time owing to thee'longation of the wire 19. From then on the contacts 11, .12' are closed already before the wire 19 1123 regained its original Thus, the minimum temperature of the wire 19- length. must be higher to give the wire a new minimum length. corresponding to the new position of the contact 12, and owing to this higher temperature the heat emission of the wire to the surrounding atmosphere becomes greater. consequently, the periods of closed current become feeler body.

Every time the contacts areopened or closed a great momentary increase of the field intensity in the ironcore The vibrator described therefore operate at a very varying amplitudathe smallest" value of which is determined solely by the peakvaluesof of the transformer occurs.

the alternating current, whil'ethe'highest amplitude value is obtained when such a peak value coincides with a maxi-- mum value of the field intensity genera-ted at the breaking or-closingof the circuit. Owing to this varying amplitude around the feeler body 24 25. The Contact 12 is then moved slightly downwards in Figure l in the direcwhich constitutes a the-vibrating contact 12 will, on-differe'nt occasions, hit ditferent' parts'of the surface of thecontact 11, and also this circumstance contributes to a good contact" and a responsive element, an clectromagnet energized by a separate, alternating current circuit and also energized by current pulses passing through said circuit containing said cooperating contacts, and a member of magnetic metal secured to one of said contacts and positioned in thefield offorce of the electromagnet to be vibrated ina direction substantially perpendicular to a line passing through both contacts. j r j 2. In an electric indicating apparatus *for indicating pressures, temperatures; the position ofa body in'r'notion, and similar magnitudes, said apparatus having an alternating current circuit, a motion'transm-itting member arranged'to be acted upon by the magnitude to be measured, a .thermoresponsive heating element subjected to variations in length when heated, means for heating said element when current passes through said circuit, and a pointer instrument connected to show a deflection depending on the efiective valueof the current pulses produced n'the circuit, the combination of a first and a second movable contact connected in said circuit and cooperating with each other, the first, contact'being supported'by saidrnotion transmitting member, the position of said first contact thereby being adjustable in relation to the second contact, a resilient member supporting the second contact immediately inifront of said first contact and connected to said thermoresponsive element'to cause the second contact to open and close the circuit depending-on the variationsin the length of said thermore sponsive element, a transformer havingan iron core a primary and a secondary winding, said secondary winding constituting the low voltage winding of the transformer, said secondary winding being connected in said circuit and said primary winding being energized by a separatealternating current circuit, a resistance short-circuiting said circuit between" said contacts and one end of the secondary winding of the transformer, and a member of magnetic metal seciire d to of said contacts and positioned in the field of force of the iron core to be vibrated in a direction substantially perpendicular to a line passing through both contacts.

3. In an electric indicating apparatus for indicating pressures, temperatures, the position of a body in motion, and similar magnitudes, said apparatus having an alternating current circuit, a motion transmitting member arranged to .be acted upon by the magnitude to be measured, a thennoresponsive heating element subjected to variations in length when heated, means for heating said element when current passes through said circuit, and a pointer instrument connected to show a deflection depending on the effective value of the current pulses produced in the circuit, the combination of a first and a second movable contact connected in said circuit and cooperating with each other, the first contact being supported by said motion transmitting member, the position of said first contact thereby being adjustable in relation to the second contact, a resilient member supporting the second contact immediately in front of said first contact and connected to said thermoresponsive element to cause the second contact to open and close the circuit depending on the variations in the length of said thermoresponsive element, a transformer having an iron core, a

6 primary and a secondary winding, said secondary winding constituting the low voltage winding of the transformer, said secondary winding being connected in said circuit and the primary winding being energized by a separate alternating current circuit, a resistance shortcircuiting said circuit between said contacts and one end of the secondary winding of the transformer, said transformer core having a gap therein forming an air space in the field of force of the transformer, and a plate of magnetic metal secured to one of said contacts and located immediately in front of said air space to be vibrated in a direction substantially perpendicular to a line passing through both contacts.

4. An electrothermic indicating apparatus according to claim 3, in which said plate is resiliently mounted on the motion transmitting member acted upon by the magnitude to be measured.

References Cited in the file of this patent UNITED STATES PATENTS 

